Pyrrolidine and piperidine-2-carboxylic acid derivatives

ABSTRACT

New derivatives of amino acids which have the general formula ##STR1## are useful as angiotensin converting enzyme inhibitors.

SUMMARY OF THE INVENTION

This invention relates to new derivatives of amino acids which have thegeneral formula ##STR2## and salts thereof, WHEREIN R is hydroxy orlower alkoxy; R₁ is hydrogen, lower alkanoyl, benzoyl or ##STR3## A ishydrogen, lower alkyl or hydroxy-lower alkylene; B is hydrogen, loweralkyl, phenyl, phenyl-lower alkylene, hydroxy-lower alkylene,hydroxyphenyl-lower alkylene, amino-lower alkylene, quanidino-loweralkylene, mercapto-lower alkylene, lower alkyl-thio-lower alkylene,imidazolyl-lower alkylene, indolyl-lower alkylene, carbamoyl-loweralkylene or carboxy-lower alkylene, or A and B together form a (CH₂)_(p)bridge which completes a ring of 5 or 6 atoms with the nitrogen andcarbon to which they are joined, one carbon optionally bearing a hydroxygroup;

X is carboxy, lower alkoxycarbonyl, carbamoyl, N-substituted carbamoylor cyano;

m is 0 or 1;

n is 0, 1, 2, 3 or 4; and

p is 3 or 4.

The asterisks denote centers of asymmetry.

DETAILED DESCRIPTION OF THE INVENTION

The invention includes substituted derivatives of amino acids havingformula I above.

Compounds in the group represented by formula I which are derived fromor include the structure of the amino acids glycine, alanine, leucine,threonine, phenylglycine, phenylalanine, lysine, arginine, glutamine,histidine, methionine, serine, cysteine, tyrosine, valine, asparagine,glutamic acid, proline, hydroxyproline, or tryptophane are broadlypreferred. Preferred modifications are compounds of formula I wherein Ris hydroxy; R₁ is hydrogen or lower alkanoyl (particularly hydrogen oracetyl);

X is lower alkoxycarbonyl or carbamoyl; A is hydrogen or joins in a 5-or 6-membered ring with B, especially a 5-membered ring; B is loweralkyl, amino-lower alkylene or phenyl-lower alkylene or joins in a ringwith A, especially a 5-membered ring; m is 1; and n is 1 or 2.

Especially preferred are those compounds of formula I which are derivedfrom proline and have the formula ##STR4## The symbols have the samepreferred meanings described above.

The lower alkyl groups repesented by any of the variables includestraight and branched chain hydrocarbon radicals from methyl to heptyl,for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl,pentyl, isopentyl and the like. The lower alkylene groups are of thesame kind also having 1 to 7 carbons. Similarly, the lower alkoxy groupsare of the same kind with a link to oxygen, for example, methoxy,ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, t-butoxy and the like.The C₁ -C₄ members, especially C₁ and C₂ members, of all types arepreferred. Phenylmethyl is the preferred phenyl-lower alkylene group andmethoxy and t-butoxy the preferred lower alkoxy groups. The loweralkanoyl groups are the acyl radicals of the lower (up to 7 carbons)fatty acids, e.g., acetyl, propionyl, butyryl and the like, acetyl beingpreferred.

The N-substituted carbamoyl groups represented by X are carbamoylradicals bearing on the nitrogen a lower alkyl or a phenyl-loweralkylene substituent.

The products of formula I and the preferred subgroups can be produced byvarious methods of synthesis.

According to a preferred method, the amino acid of the formula ##STR5##wherein A and B are defined as above, and R is hydroxy is acylated withan acid of the formula ##STR6## wherein R₁, m and n have the meaningdefined above and X is other than carboxyl, by one of the knownprocedures in which the acid IV is activated, prior to reaction with theacid III, involving formation of a mixed anhydride, symmetricalanhydride, acid chloride, active ester, Woodward reagent K,N,N'-carbonylbisimidazole, EEDQ(N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline) or the like. When R islower alkoxy, this or other known methods of coupling such moieties canbe used. [For a review of these methods, see Methoden der OrganischenChemie(Houben-Weyl) Vol. XV, parts 1 and 2(1974)].

Compounds of formula I wherein X is --CONH₂ and R is hydroxy can also beproduced by ammonolysis of those compounds of formula I wherein X islower alkoxycarbonyl.

Compounds of formula I wherein m is 0 can also be produced by acylationof the acid of formula II with an acid of the formula ##STR7## whereinHal represents halogen, preferably chlorine or bromine, followed bydisplacement with a thiol acid of the formula

(VI) R-COSH

When the product obtained is an ester, e.g., R₁ is lower alkoxy, theester can be converted to the free carboxy group by saponification or,when R₁ is a tertiary lower alkoxy group, e.g., t-but oxy, by treatmentwith trifluoroacetic acid and anisole. Conversely the free acid can beesterified by conventional procedures.

The disulfides of formula I, wherein R₁ is ##STR8## are obtained byoxidation of the compound of the formula ##STR9## e.g., with analcoholic solution of iodine.

Products of formula I have two asymmetric carbon atoms. These carbonatoms are indicated by an asterisk in formula I. The compoundsaccordingly exist in diastereoisomeric forms or in racemic mixturesthereof. All of these are within the scope of the invention. The abovedescribed syntheses can utilize the racemate or one of the enantiomersas starting material. When the racemic starting material is used in thesynthetic procedure, the stereoisomers obtained in the product can beseparated by conventional chromatographic or fractional crystallizationmethods. In general, the L-isomer with respect to the carbon of theamino acid constitutes the preferred isomeric form.

The compounds of this invention form basic salts with various inorganicand organic bases which are also within the scope of the invention. Suchsalts include ammonium salts, alkali metal salts like sodium andpotassium salts (which are preferred), alkaline earth metal salts likethe calcium and magnesium salts, salts with organic bases, e.g.,dicyclohexylamine salt, benzathine, N-methyl-D-glucamine, hydrabaminesalts, salts with amino acids like arginine, lysine and the like. Thenon-toxic, physiologically acceptable salts are preferred, althoughother salts are also useful, e.g., in isolating or purifying theproduct.

The salts are formed in conventional manner by reacting the free acidform of the product with one or more equivalents of the appropriate baseproviding the desired cation in a solvent or medium in which the salt isinsoluble, or in water and removing the water by freeze drying. Byneutralizing the salt with an insoluble acid like a cation exchangeresin in the hydrogen form [e.g., polystyrene sulfonic acid resin --Dowex 50 (Mikes, Laboratory Handbook of Chromatographic Methods (VanNostrand, 1961) page 256] or with an aqueous acid and extraction with anorganic solvent, e.g., ethyl acetate, dichloromethane or the like, thefree acid form can be obtained, and, if desired, another salt formed.

Additional experimental details are found in the examples which arepreferred embodiments and also serve as models for the preparation ofother members of the group.

The compounds of this invention inhibit the conversion of thedecapeptide angiotensin I to angiotensin II and therefore are useful inreducing or relieving angiotensin related hypertension. The action ofthe enzyme renin or angiotensinogen, a pseudoglobulin in blood plasma,produces angiotensin I. Angiotensin I is converted by angiotensinconverting enzyme (ACE) to angiotensin II. The latter is an activepressor substance present which has been implicated as the causativeagent in various forms of hypertension in various mammalian species,e.g., rats, dogs, etc. The compounds of this invention intervene in theangiotensinogen → angiotensin I → angiotensin II sequence by inhibitingangiotensin converting enzyme and reducing or eliminating the formationof the pressor substance angiotensin II.

The inhibition of the angiotensin converting enzyme by compounds offormula I can be measured in vitro with isolated angiotensin convertingenzyme from rabbit lungs following the procedure described by Cushmanand Cheung [Biochem. Pharmacol., 20, 1637 (1971)], and with an excisedsmooth muscle assay [E. O'Keefe, et al., Federation Proc. 31, 511(1972)] in which these compounds have been shown to be powerfulinhibitors of the contractile activity of angiotensin I and potentiatorsof the contractile activity of bradykinin.

The administration of a composition containing one or a combination ofcompounds of formula I or physiologically acceptable salt thereof to thespecies of hypertensive mammal alleviates or reduces angiotensindependent hypertension. A single dose, or preferably two to four divideddaily doses, provided on a basis of about 5 to 1000 mg. per kilogram perday, preferably about 10 to 500 mg. per kilogram per day is appropriateto reduce blood pressure. The animal model experiments described by S.L. Engel, T. R. Schaeffer, M. H. Waugh and B. Rubin, Proc. Soc. Exp.Biol. Med. 143, (1973) serve as a useful guide.

The substance is preferably administered orally, but parenteral routessuch as subcutaneously, intramuscularly, intravenously orintraperitoneally can also be employed.

The compounds of this invention can be utilized to achieve the reductionof blood pressure by formulating in composition such as tablets,capsules or elixirs for oral administration or in sterile solution orsuspensions for parenteral administration. About 10 to 500 mg. of acompound or mixture of compounds of formula I or physiologicallyacceptable salt is compounded with a physiologically acceptable vehicle,carrier, excipient, binder, preservative, stabilizer, flavor, etc., in aunit dosage form as called for by accepted pharmaceutical practice. Theamount of active substance in these compositions or preparations is suchthat a suitable dosage in the range indicated is obtained.

The following examples are illustrative of the invention. Alltemperatures are in degrees celsius.

EXAMPLE 1 3-Acetylthio-2-methoxycarbonylmethylpropanoic acid

A mixture of thiolacetic acid (12.5 g.) and3-methoxycarbonyl-2-methylenepropanoic acid (17.1 g.) are heated on thesteam bath for two hours. The reaction is concentrated in vacuo and theresidue is dissolved in ethyl acetate (125 ml.) and dicyclohexylamine(35 ml.) is added. The crystals are filtered, dried and recrystallizedfrom ethyl acetate to yield 37.8 g., m.p. 120°-121°. Thisdicyclohexylammonium salt of3-acetylthio-2-methoxycarbonylmethylpropanoic acid is converted to thefree acid by distribution between a system of ethyl acetate and 10%aqueous potassium bisulfate.

EXAMPLE 21-[3-(Acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-prolinetert-butyl ester

To a solution of L-proline tert-butyl ester (1.71 g.) and3-hydroxybenzotriazole (1.35 g.) in dichloromethane (15 ml.),dicyclohexylcarbodiimide (2.06 g.) and3-acetylthio-2-methoxycarbonylmethylpropanoic acid (2.2 g.) are added.After 18 hours stirring at room temperature, the precipitate formed isfiltered off, the filtrate is washed neutral, dried, and concentrated todryness to yield 3.7 g. of1-[3-(acetylthio)-2-(methoxycarbonylmethyl)-propanoyl]-L-prolinetert-butyl ester Rf: 0.8 (silica gel-ethyl acetate).

EXAMPLE 31-[3-(Acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-proline

1-[3-(Acetylthio)-2-(methoxycarbonylmetnyl)propanoyl]-L-prolinetert-butyl ester (2.9 g.) is dissolved in a mixture of trifluoroaceticacid (17.5 ml.) and anisole (8.4 ml.). After one hour storage at roomtemperature the excess trifluoroacetic acid is removed in vacuo and theresidue is precipitated twice from ether-hexane to yield 2.1 g. of1-[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-proline Rf: 0.4(silica gel-benzene:acetic acid 75:25).

EXAMPLE 4 1-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl] -L-proline

1-[3-(Acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-proline (2.1 g.)is dissolved in a mixture of water (35 ml.) and concentrated ammonia (35ml.) under a blanket of argon. After 20 minutes, the solution is chilledin an ice bath, made acidic with concentrated hydrochloric acid,saturated with sodium chloride and extracted with ethyl acetate. Theorganic layer is dried and concentrated to dryness in vacuo to yield 1.1g. of 1-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-proline thatis purified by chromatography on silica gel (benzene:acetic acid 75:25).R_(f) : 0.35 (silica gel, benzene:acetic acid, 75:25).

EXAMPLE 5 1-[2-Carboxymethyl-3-mercaptopropanoyl]-L-proline

To a solution of1-[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-proline (3 g.)in methanol (60 ml.), N sodium hydroxide (60 ml.) is added. After 4hours, the solution is applied to a column of Dowex 50 ion exchangeresin in the hydrogen cycle, and the desired material is eluted withwater to yield 2.3 g. of1-[2-carboxymethyl-3-mercaptopropanoyl]-L-proline R_(f) : 0.2 (silicagel, benzene:acetic acid 75:25).

EXAMPLE 6 1-[2-Carbamoylmethyl-3-mercaptopropanoyl]-L-proline

A. 1-[3-(Acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-proline (2.1g.) is dissolved in a mixture of water (40 ml.) and concentrated ammonia(40 ml.). After one hour the reaction mixture is concentrated to 1/3volume, and applied to a column of Dowex 50 resin in the hydrogen cycle.The product is eluted with water. The aqueous is extracted with ethylacetate and then concentrated to dryness to yield 1.4 g. of1-[2-carbamoylmethyl-3-mercaptopropanoyl]-L-proline R_(f) : 0.50 (silicagel, chloroform:methanol:acetic acid:water).

B. 1-[2-Carbamoylmethyl-3-acetylthiopropanoyl]-L-proline (1.2 g.) isdissolved in a mixture of water (20ml.) and concentrated ammonia (20ml.). After 15 minutes the reaction mixture is processed as described in"A" above to obtain 1-[2-carbamoylmethyl-3-mercaptopropanoyl]-L-proline.

EXAMPLE 7 3-Acetylthio-2-carbamoylmethylpropanoic acid

By substituting 3-carbamoyl-2-methylenepropanoic acid for the3-methoxycarbonyl-2-methylenepropanoic acid in the procedure of Example1, 3-acetylthio-2-carbamoylmethylpropanoic acid is obtained, m.p.110°-111°.

EXAMPLE 8 3-Acetylthio-2-cyanomethylpropanoic acid

Dicyclohexylcarbodiimide (1.03 g.) is added to a solution of3-acetylthio-2-carbamoylmethylpropanoic acid (1.02 g.) in pyridine (18ml.). After 5 hours stirring at room temperature, the precipitate isfiltered off and the filtrate is concentrated to dryness, the residue isdissolved in ethyl acetate and extracted with saturated aqueousbicarbonate. The aqueous phase is acidified and extracted with ethylacetate. This organic layer is dried and concentrated to dryness. Theresidue, 3-acetylthio-2-cyanomethylpropanoic acid is crystallized fromether-hexane, m.p. 110°-112°.

EXAMPLE 9 3-Acetylthio-2-(methoxycarbonylmethyl)propanoic acidN-hydroxysuccinimido ester

To a solution of 3-acetylthio-2-(methoxycarbonylmethyl)propanoic acid(5.5 g.) and N-hydroxysuccinimide (2.9 g.) in tetrahydrofuran (100 ml.)chilled in an ice bath, dicyclohexylcarbodiimide (5.15 g.) is added. Thereaction mixture is stirred for 15 hours at 5°, filtered and thefiltrate is concentrated to dryness in vacuo to yield3-acetylthio-2-(methoxycarbonylmethyl)propanoic acidN-hydroxysuccinimido ester.

EXAMPLE 10 1-[2-(Carbamoylmethyl)-3-(acetylthio)propanoyl]-L-proline

By substituting 3-acetylthio-2-(carbamoylmethyl)propanoic acid for the3-(acetylthio)-2-(methoxycarbonylmethyl)propanoic acid in the procedureof Example 2, and then submitting the product to the procedure ofExample 3, 1-[2-(carbamoylmethyl)-3-(acetylthio)propanoyl]-L-prolinetert-butyl ester and1-[2-(carbamoylmethyl)-3-(acetylthio)propanoyl]-L-proline are obtained.

EXAMPLE 11 3-Acetylthio-2-[(N-butylcarbamoyl)methyl]propanoic acid

By substituting 3-(N-butylcarbamoyl)-2-methylenepropanoic acid for the3-methoxycarbonyl-2-methylenepropanoic acid in the procedure of Example1, 3-acetylthio-2-[(N-butylcarbamoyl)methyl]propanoic acid is obtained.

EXAMPLE 121-[3-(Acetylthio)-2-[(N-butylcarbamoyl)methyl]propanoyl]-L-proline

By substituting 3-(acetylthio)-2-[(N-butylcarbamoyl)methyl]propanoicacid for the 3-(acetylthio)-2-(methoxycarbonylmethyl)propanoic acid inthe procedure of Example 2 and then submitting the product to theprocedure of Example 3,1-[3-(acetylthio)-2-[(N-butylcarbamoyl)methyl]propanyl]-L-proline isobtained.

EXAMPLE 13 2-Methylene-4-(ethoxycarbonyl)butyric acid

A mixture of 2-methyleneglutaric acid [Ber. 34, 427 (1901)] (40 g.) andacetyl chloride (80 ml.) is heated on the steam bath for 1.5 hours. Theexcess acetyl chloride is removed in vacuo (75°) and the residue isevaporated from toluene twice. Finally, the residue is dissolved inethanol and heated on the steam bath for 1 hour. The reaction mixture isconcentrated to dryness to yield 2-methylene-4-(ethoxycarbonyl)butyricacid.

EXAMPLE 14 1-[2-Mercaptomethyl-4-(ethoxycarbonyl)butanoyl]-L-proline

By substituting 2-methylene-4-(ethoxycarbonyl)butyric acid for the3-methoxycarbonyl-2-methylenepropanoic acid in the procedure of Example1, and then submitting the product to the procedure of Examples 2, 3 and4, 2-acetylthiomethyl-4-(ethoxycarbonyl)butyric acid,1-[2-(acetylthio)methyl-4-(ethoxycarbonyl)butanoyl]-L-proline tert-butylester, 1-[2-(acetylthiomethyl)-4-(ethoxycarbonyl)butanoyl]-L-proline and1-[2-mercaptomethyl-4-(ethoxycarbonyl)butanoyl]-L-proline are obtained.

EXAMPLE 15 1-[3-Mercapto-2-(cyanomethyl)propanoyl]-L-proline

By substituting 3-acetylthio-2-cyanomethylpropanoic acid for the3-(acetylthio)-2-(methoxycarbonylmethyl)propanoic acid in the procedureof Example 2, and then submitting the product to the procedures ofExamples 3 and 4, 1-[3-(acetylthio)-2-(cyanomethyl)propanoyl]-L-prolinetert-butyl ester, 1-[3-(acetylthio)-2-(cyanomethyl)propanoyl]-L-prolineand 1-[3-mercapto-2-(cyanomethyl)propanoyl]-L-proline are obtained.

By treating this product with an equivalent proportion of sodiumhydroxide solution, then removing the water by freeze drying, the sodiumsalt is obtained.

EXAMPLE 161,1'-[Dithiobis-[2-(methoxycarbonylmethyl)-3-propanoyl]]-bis-L-proline

To a solution of1-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-proline (1 g.) inwater (20 ml.), an alcoholic solution of iodine is added untilpersistent yellow color, while maintaining the pH between 5 and 7 bycareful addition of N sodium hydroxide. The yellow color is dischargedby addition of a few drops of aqueous sodium thiosulfate and afteracidification with concentrated hydrochloric acid, the reaction mixtureis extracted with ethyl acetate. The organic layer is dried andconcentrated to dryness in vacuo to yield1,1'-[dithiobis-[2-(methoxycarbonylmethyl)3-propanoyl]]-bis-L-proline.

EXAMPLE 17 N.sup.α-[3-(Acetylthio)-2-methoxycarbonylmethyl)propanoyl]-L-arginine

A solution of 3-(acetylthio)-2-(methoxycarbonylmethyl)propanoic acidN-hydroxysuccinimide ester (1.67 g.) in ethanol (17 ml.) is addeddropwise to a solution of L-arginine (0.9 g.), and sodium bicarbonate(1.26 g.) in water (12 ml.). The mixture is stirred at room temperaturefor 16 hours, and then extracted with ethyl acetate. The aqueous layeris applied to a column of Dowex 50 resin in the hydrogen cycle, andeluted with water until no more acidic material is eluted. N.sup.α-[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-arginine is theneluted with pyridine-acetate buffer at pH 6.5.

EXAMPLE 18 N.sup.α-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-arginine

To a solution of N.sup.α-[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-arginine (1.9 g.)in methanol (10 ml.), sodium methoxide (0.56 g.) is added. After tenminutes, the solution is applied to a column of Dowex 50 resin and thecolumn is washed with water until no more acidic material is eluted.N.sup.α -[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-arginine isthen eluted with a pyridine-acetate buffer of pH 6.5.

EXAMPLE 19 N.sup.α -[-Mercapto-2-(carbamoylmethyl)propanoyl]-L-arginine

By substituting N.sup.α-[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-arginine for the1-[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-proline in theprocedure of Example 6A, and then isolating the product with Dowex 50resin as described in the procedure of Example 17, N.sup.α-[3-mercapto-2-(carbamoylmethyl)propanoyl]-L-arginine is obtained.

EXAMPLE 20 N.sup.α-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-histidine

By substituting L-histidine for the L-arginine in the procedure ofExample 17, and then submitting the product to the procedure of Example18, N.sup.α-[3-(acetylthio)-2-methoxycarbonylmethyl)propanoyl]-L-histidine andN.sup.α -[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-histidine areobtained.

EXAMPLE 21 N.sup.α-[3-Mercapto-2-(carbamoylmethyl)propanoyl]-L-histidine

By substituting N.sup.α-[3-(acetylthio)-2-methoxycarbonylmethyl)propanoyl]-L-histidine for theN.sup.α -[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-argininein the procedure of Example 19, N.sup.α-[3-mercapto-2-(carbamoylmethyl)propanoyl]-L-histidine is obtained.

EXAMPLE 22 N-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-alanine

By substituting L-alanine tert-butyl ester for the L-proline tert-butylester in the procedure of Example 2, and then submitting the product tothe procedure of Examples 3 and 4,N-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-alanine is obtained.

EXAMPLE 23 N-[2-(Carbamoylmethyl)-3-mercaptopropanoyl]-L-alanine

By substituting L-alanine tert-butyl ester for the L-proline tert-butylester in the procedure of Example 2, and then submitting the product tothe procedures of Examples 3 and 6,N-[2-(carbamoylmethyl)-3-mercaptopropanoyl]-L-alanine is obtained.

EXAMPLE 24N-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-asparagine

By substituting L-asparagine tert-butyl ester for the L-prolinetert-butyl ester in the procedure of Example 2, and then submitting theproduct to the procedure of Examples 3 and4N-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-asparagine isobtained.

EXAMPLE 25 N-[2-(Carbamoylmethyl)-3-mercaptopropanoyl]-L-glutamine

By substituting L-glutamine tert-butyl ester for the L-prolinetert-butyl ester in the procedure of Example 2, and then submitting theproduct to the procedures of Examples 3 and 6A,N-[2-carbamoylmethyl)-3-mercaptopropanoyl]-L-glutamine is obtained.

EXAMPLE 26 N-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-asparticacid

By substituting L-aspartic acid di-tert-butyl ester for the L-prolinetert-butyl ester in the procedure of Example 2, and them submitting theproduct to the procedure of Examples 3 and 4,N-[3-mercapto-2-(methoxycarbonylmethyl)-propanoyl]-L-aspartic acid isobtained.

EXAMPLE 27 N-[2-(Carbamoylmethyl)-3-mercaptopropanoyl]-L-glutamic acid

By substituting L-glutamic acid di-tert-butyl ester for the L-prolinetert-butyl ester in the procedure of Example 2, and then submitting theproduct to the pocedure of Examples 3 and 6A, N-[2-(carbomoylmethyl)-3-mercaptopropanoyl]-L-glutamic acid is obtained.

EXAMPLE 28N-[3-(Acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-S-(N-ethylcarbamoyl)-L-cysteine

A solution of 3-(acetylthio)-2-(methoxycarbonylmethyl)-propanoic acidN-hydroxysuccinimido ester (1.67 g.) in ethanol (17 ml.) is addeddropwise to a solution of S-(N-ethylcarbamoyl)-L-cysteine (1g.) andsodium bicarbonate (1.26 g.) in water (12 ml.). The mixture is stirredat room temperature for sixteen hours and then is extracted with ethylacetate. The aqueous layer is acidified and extracted with ethylacetate. This second organic layer is dried and concentrated to drynessin vacuo to yield N-[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-S-(N-ethylcarbamoyl)-L-cysteine.

EXAMPLE 29 N-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-cysteine

To a solution ofN-[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-S-(N-ethylcarbamoyl)-L-cysteine(1.9 g.) in methanol (10 ml.), sodium methoxide (0.84 g.) is added.After 30 minutes, the solution is diluted with 0.1 N hydrochloric acidand extracted with ethyl acetate. The organic layer is dried andconcentrated to dryness in vacuo to yieldN-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-cysteine.

EXAMPLE 30 N.sup.α-[3-(Acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-lysine

By substituting N.sup.ε -tert-butyloxycarbonyl-L-lysine tert-butyl esterfor the L-proline tert-butyl ester in the procedure of Example 3,followed by isolation with Dowex 50 resin as described in Example 17,N.sup.α -[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-lysine isobtained.

EXAMPLE 31 N.sup.α-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-lysine

By substituting N.sup.α-[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-lysine for theN.sup.α -[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-argininein the procedure of Example 18, N.sup.α-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-lysine is obtained.

Example 32 N.sup.α -[2-(Carbamoylmethyl)-3-mercaptopropanoyl]-L-lysine

By substituting N.sup.α-[3-(acethylthio)-2-methoxycarbonylmethylpropanoyl]-L-lysine for theN.sup.α -[3-acetylthio-2-methoxycarbonylmethylpropanoyl]-L-arginine inthe procedure of Example 19, N.sup.α-[2-(carbamoylmethyl)-3-mercaptopropanoyl]-L-lysine is obtained.

Example 33N-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-methionine

By substituting L-methionine diphenylmethyl ester for the L-prolinetert-butyl ester in the procedure of Example 2, and then submitting theproduct to the procedure of Examples 3 and 4,N-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-methionine isobtained.

Example 34 N-[2-(Carbamoylmethyl)-3-mercaptopropanoyl]-L-methionine

By substituting L-methionine diphenylmethyl ester for the L-prolinetert-butyl ester in the procedure of Example 2, and then submitting theproduct to the procedure of Examples 3 and 6A,N-[2-(carbamoylmethyl)-3-mercaptopropanoyl]-L-methionine is obtained.

Example 35N-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-phenylalanine

By substituting L-phenylalanine tert-butyl ester for the L-prolinetert-butyl ester in the procedure of Example 2, and then submitting theproduct to the procedure of Examples 3 and 4,N-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-phenylalanine isobtained.

Example 36 N-[2(Carbamoylmethyl)-3-mercaptopropanoyl]-L-phenylalanine

By substituting L-phenylalanine tert-butyl ester for the L-prolinetert-butyl ester in the procedure of Example 2, and then submitting theproduct to the procedure of Examples 3 and 6A,N-[2-(carbamoylmethyl)-3-mercaptopropanoyl]-L-phenylalanine is obtained.

Example 371-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-4-hydroxy-L-proline

By substituting 4-hydroxy-L-proline p-methoxybenzyl ester for theL-proline tert-butyl ester in the procedure of Example 2, and thensubmitting the product to the procedures of Examples 3 and 4,1-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-4-hydroxy-L-proline isobtained.

Example 381-[2-Carbamoylmethyl-3-mercaptopropanoyl]-5-hydroxy-L-pipecolic acid

By substituting 5-hydroxy-L-pipecolic acid for theS-(N-ethylcarbamoyl)-L-cysteine in the procedure of Example 28, and thensubmitting the product to the procedure of Example 6A,1-[2-carbamoylmethyl-3-mercaptopropanoyl]-5-hydroxy-L-pipecolic acid isobtained.

Example 39 1-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-pipecolicacid

By substituting L-pipecolic acid tert-butyl ester (prepared fromL-pipecolic acid as described for L-proline) for the L-prolinetert-butyl ester in the procedure of Example 2, and then submitting theproduct to the procedure of Examples 3 and 4,1-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-pipecolic acid isobtained.

Example 40 N-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-serine

By substituting O-tert-butyl-L-serine tert-butyl ester for the L-prolinetert-butyl ester in the procedure of Example 2, and then submitting theproduct to the procedure of Examples 3 and 4,N-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-serine is obtained.

Example " N-[2-(Carbamoylmethyl)-3-mercaptopropanoyl]-L-threonine

By substituting O-tert-butyl-L-threonine tert-butyl ester for theL-proline tert-butyl ester in the procedure of Example 2, and thensubmitting the product to the procedures of Examples 3 and 6A,N-[2-(carbamoylmethyl)-3-mercaptopropanoyl]-L-threonine is obtained.

Example 42 N-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-tyrosine

By substituting L-tyrosine for the S-(N-ethylcarbamoyl)-L-cysteine inthe procedure of Example 28, and then submitting the product to theprocedure of Example 29,N-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-tyrosine isobtained.

Example 43 N.sup.α-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-tryptophane

By submitting L-tryptophane for the S-(N-ethylcarbamoyl)-L-cysteine inthe procedure of Example 28, and then submitting the product to theprocedure of Example 29, N.sup.α-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-tryptophane isobtained.

Example 44 N.sup.α ,N.sup.α-[Dithiobis-(2-methoxycarbonylmethyl)-3-propanoyl]-bis-L-lysine

By substituting N.sup.α-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-lysine for the1-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-L-proline in theprocedure of Example 16, and isolating the product with a Dowex 50 resinas described in the procedure of Example 18, N.sup.α,N.sup.α-[dithiobis-(2-methoxycarbonylmethyl)-3-propanoyl]-bis-L-lysine isobtained.

Example 45 1-[2-(Benzoylthio)-3-(methoxycarbonyl)propanoyl]-L-proline

L-Proline (5.75 g.) is dissolved in aqueous N sodium hydroxide (50 ml.)and the solution is chilled in an ice bath with stirring. 2N Sodiumhydroxide (25 ml.) and 2-bromo-3-(methoxycarbonyl)propionyl chloride(11.6 g.) are added in that order and the mixture is removed from theice bath and stirred at room temperature for 1 hour. A mixture ofthiobenzoic acid (7.5 g.) and potassium carbonate (4.8 g.) in water (50ml.) is added and the mixture is stirred overnight at room temperature.After acidification with concentrated hydrochloric acid, the aqueoussolution is extracted with ethyl acetate and the organic phase is washedwith water, dried and concentrated to dryness to give1-[2-(benzoylthio)-3-(methoxycarbonyl)propanoyl]-L-proline.

Example 46 1-[2-Mercapto-3-(methoxycarbonylmethyl)propanoyl]-L-proline

By substituting1-[2-(benzoylthio)-3-(methoxycarbonyl)propanoyl]-L-proline for the1-[3-(acetylthio)-2-(methoxycarbonylmethyl)propanoyl]-L-proline in theprocedure of Example 4,1-[2-mercapto-3-(methoxycarbonylmethyl)propanoyl]-L-proline is obtained.

Example 47N-[3-Mercapto-2-(methoxycarbonylmethyl)propanoyl]-N-methyl-L-phenylalanine

By substituting N-methyl-L-phenylalanine for theS-(N-ethylcarbamoyl)-L-cysteine in the procedure of Example 28, and thensubmitting the product to the procedure of Example 29,N-[3-mercapto-2-(methoxycarbonylmethyl)propanoyl]-N-methyl-L-phenylalanineis obtained.

Example 48 1-[3-Acetylthio-2-(cyanomethyl)propanoyl]-L-proline

1-[3-Acetylthio-2-(cyanomethyl)propanoyl]-L-proline tert butyl ester(2.1 g.) and p-toluene sulfonic acid (0.500 g.) are dissolved in benzene(25 ml.) and the solution is refluxed for 30 minutes. The solvent isremoved in vacuo, the residue is dissolved in ethyl acetate, washedtwice with water, dried and concentrated to dryness. The residue ischromatographed on silica gel with benzene: acetic acid (75:25), yield0.85 g. R_(f) : 0.18 (silica gel:benzene:acetic acid 75:25).

What is claimed is:
 1. A compound of the formula ##STR10## and salts thereof, wherein R is hydroxy or lower alkoxy; R₁ is hydrogen, lower alkanoyl, benzoyl or ##STR11## A and B together form a (CH₂)_(p) bridge which completes an unsubstituted ring of 5 or 6 atoms with the nitrogen and carbon to which they are joined or said ring substituted with a hydroxy group;X is carboxy, lower alkoxycarbonyl, carbamoyl, N-substituted carbamoyl wherein N-substituent is lower alkyl or phenyl-lower alkylene, or cyano: m is 0 or 1; n is 0, 1, 2, 3 or 4; and p is 3 or
 4. 2. A compound as in claim 1 wherein R is hydroxy; R₁ is hydrogen or lower alkanoyl; X is lower alkoxycarbonyl or carbamoyl; A and B join to complete a 5- or 6-membered ring; m is 1 and n is 1 or
 2. 3. A compound of the formula ##STR12## and salts thereof, wherein R, R₁, X, m and n have the same meaning as in claim
 1. 4. A compound of the formula ##STR13## and salts thereof, wherein R, R₁, X, m and n have the same meaning as in claim
 2. 5. A compound as in claim 1 wherein ##STR14## is the radical of proline or hydroxyproline.
 6. A compound as in claim 1 wherein A and B together are --(CH₂)₄ completing a six-membered ring.
 7. A compound as in claim 1 wherein R₁ is ##STR15##
 8. A compound as in claim 1 wherein X is carboxy.
 9. A compound as in claim 1 wherein X is lower alkoxycarbonyl.
 10. A compound as in claim 1 wherein X is carbamoyl.
 11. A compound as in claim 1 wherein X is cyano.
 12. A compound as in claim 3 wherein R is hydroxy; R₁ is hydrogen; X is methoxycarbonyl; and m and n each is
 1. 13. A compound as in claim 3 wherein R is hydroxy; R₁ is hydrogen; X is carbamoyl; and n and m each is
 1. 14. A compound as in claim 3 wherein R is hydroxy; R₁ is hydrogen; X is cyano; and m and n each is
 1. 